Converting Matrices to translations and back changes geometry in Animation Nodes
A matrix represents a translation, a rotation and a scale.

When you create matrices on a circle, each will have a different translation and rotation. When you decompose the matrices and only use the translational part to create the new matrices, the rotation is lost in the process.

Instead of using the Translation Matrix node you could use the Compose Matrix node. This way you can use the rotations of the old matrices in the new ones as well.

If you just want to move every matrix a little bit, I recommend to use the Offset Matrices node instead of doing all those conversions yourself.